A tiny loosely coiled shell with body whorl below the rest to create a flat spire. Whorls are traversed by radial ridges which may form conspicuous narrow keels at regular intervals. Surface pale brown, glossy but often covered with deposits. Widespread.

(Technically it has always been difficult with planorbids to decide whether the raised whorls form a spire or an umbilicus! In these accounts the raised part is called (commonsensically) a spire even even though most experts regard it as an umbilicus)

Size

2-3 mm.

World Distribution

Spread across the northern part of the whole northern hemisphere. Distribution type: Circumpolar Wide-temperate (66).

Irish Distribution

Very widespread and locally common but much under-recorded because of its size.

Ecology

A species of clear, weedy conditions in still water habitats

Common in medium to very small habitats including sluggish streams, drains and marsh or fen pools

Occasionally found in very acid waters

Habitat size appears to be little impediment to this species - a thriving colony lives in a tiny ornamental pool (3m across) at the Lion's Gate, Mussenden Temple on the north Londonderry coast in water at best 2-3cm deep